Nicolas Pinel

Modeling of the Bistatic Electromagnetic Scattering From Sea Surfaces Covered in Oil for Microwave Applications

This paper describes the influence of oil pollution over sea surfaces on the height spectrum and the height autocorrelation function of rough surfaces. An oil slick damps the capillarity waves of the surface height spectrum and reduces the root mean square slope of the surface. These modified functions then have an influence on the radar cross section (RCS) from contaminated sea surfaces. The bistatic RCS of the contaminated sea surface is then presented by comparison with a clean sea: results from a benchmark numerical model are presented and compared with a new semiempirical model using the geometric optics approximation and then the first-order smallslope approximation.

Method of Moments for 2D Scattering Problems: Basic Concepts and Applications

In this book, the method of moments (MoM) is addressed to compute the field scattered by scatterers such as canonical objects (cylinder or plate) or a randomly rough surface, and also by an object above or below a random rough surface. Because the problem is considered two-dimensional (2D), the integral equations (IEs) are scalar and only the transverse electric (TE) and transverse magnetic (TM) polarizations are considered (no cross polarizations occur). Chapter 1 analyzes how the MoM with the point matching method and pulse basic functions is applied to convert the IEs into a linear system. In addition, chapter 1 presents the statistical parameters necessary to generate Gaussian random rough surfaces. Chapter 2 compares the MoM with the exact solution of the field scattered by a circular cylinder in free space, and with the physical optics (PO) approximation for the scattering from a plate in free space. Chapter 3 presents numerical results, obtained from the MoM combined with the efficient E-PILE method, of the scattering from two illuminated scatterers and how the E-PILE algorithm can be hybridized with asymptotic or rigorous methods valid for the scattering from a single scatterer(alone). Chapter 4 presents the same results as in Chapter 3 but for an object above a random rough surface or for a coated (circular or elliptical) cylinder. In the last two chapters, the coupling between the two scatterers is also studied in detail by inverting the impedance matrix by blocks.

A Geometrical Optics Model of Three Dimensional Scattering From a Rough Layer With Two Rough Surfaces

An asymptotic method is described for predicting the bistatic normalized radar cross section of a rough homogeneous layer made up of two rough surfaces. The model is based on iteration of the Kirchhoff approximation to calculate the fields scattered by the rough layer, and is reduced to the high-frequency limit in order to obtain numerical results rapidly. Shadowing effects, significant for large incidence or scattering angles, are taken into account through the use of shadowing functions. The model is applicable for moderate to large surface roughnesses having small to moderate slopes, and for both lossless and lossy inner media. It was validated for a rough layer with a rough surface over a perfectly flat surface in a preceding contribution. Here, the extension of the model to a rough layer with two rough surfaces is developed, and results are presented to validate the asymptotic model by comparison with a numerical reference method.

FORWARD RADAR PROPAGATION OVER OIL SLICKS ON SEA SURFACES USING THE AMENT MODEL WITH SHADOWING EFFECT

This paper is devoted to the forward radar propagation over clean and contaminated seas, using the Ament model and by taking the shadowing effect into account. The well-known Rayleigh parameter, which characterizes the degree of roughness of a corrugated surface for the case of reflection on a rough surface, is presented. Then, it is extended to the transmission through a rough surface, and to the reflection on a layer of two rough interfaces. This extended Rayleigh parameter allows then to calculate the forward radar propagation over oil slicks on sea surfaces, using the Ament model. Moreover, the model is improved by taking the shadowing effect into account. Numerical results of contaminated seas are presented, and compared to that of clean seas.

Scattering from very rough layers under the geometric optics approximation: further investigation

Scattering from very rough homogeneous layers is studied in the high-frequency limit (under the geometric optics approximation) by taking the shadowing effect into account. To do so, the iterated Kirchhoff approximation, recently developed by Pinel et al. [Waves Random Complex Media17, 283 (2007)] and reduced to the geometric optics approximation, is used and investigated in more detail. The contributions from the higher orders of scattering inside the rough layer are calculated under the iterated Kirchhoff approximation. The method can be applied to rough layers of either very rough or perfectly flat lower interfaces, separating either lossless or lossy media. The results are compared with the PILE (propagation-inside-layer expansion) method, recently developed by Déchamps et al. [J. Opt. Soc. Am. A23, 359 (2006)], and accelerated by the forward-backward method with spectral acceleration. They highlight that there is very good agreement between the developed method and the reference numerical method for all scattering orders and that the method can be applied to root-mean-square (RMS) heights at least down to 0.25lambda.

Bistatic scattering from one-dimensional random rough homogeneous layers in the high-frequency limit with shadowing effect

Many fast asymptotic models of electromagnetic scattering from a single rough interface have been developed over the last few years, but only a few have been developed on stacks of rough interfaces. The specific case of very rough surfaces, compared to the incident wavelength, has not been treated before, which is the context of this paper. The model starts from the iteration of the Kirchhoff approximation to calculate the fields scattered by a rough layer, and is reduced to the high-frequency limit in order to rapidly obtain numerical results. The shadowing effect, important under grazing angles, is taken into account. The model can be applied to any given slope statistics. Then, the model is compared with a reference numerical method based on the method of moments, which validates the model in the high-frequency limit for lossless and lossy inner media.

Degree of roughness of rough layers: extensions of the rayleigh roughness criterion and some applications

In the domain of electromagnetic wave propagation in the presence of rough surfaces, the Rayleigh roughness criterion is a widely- used means to estimate the degree of roughness of considered surface. In this paper, this Rayleigh roughness criterion is extended to the case of rough layers. Thus, it provides an interesting qualitative tool for estimating the degree of electromagnetic roughness of rough layers.

Two-Dimensional Radar Backscattering Modeling of Oil Slicks at Sea Based on the Model of Local Balance: Validation of Two Asymptotic Techniques for Thick Films

The problem of hydrodynamic modeling of the surfaces of oil films at sea is treated by using physical models, namely, the model of local balance and the Elfouhaily spectrum model for describing the clean sea surface. Then, this refined hydrodynamic modeling of the surfaces of contaminated seas makes it possible to derive electromagnetic modeling by considering thin oil films on the sea surface. Two simplifying approaches in dealing with this complex double-layer problem are described, called “thin-layer” and “classical” approaches. These two approaches, both having the advantage of reducing to a single-layer problem, are compared with a rigorous reference method for 2-D problems. Thus, their validity domains are analyzed in terms of incidence angle, wind speed, polarization, frequency, and oil viscosity. Finally, the polarimetric behavior of both clean and contaminated seas is analyzed; following recent work led on satellite measurements, the same features are retrieved, and the influence of incidence angle, frequency, and oil viscosity can be studied.

Energy conservation of the scattering from one-dimensional random rough surfaces in the high-frequency limit

Energy conservation of the scattering from one-dimensional strongly rough dielectric surfaces is investigated using the Kirchhoff approximation with single reflection and by taking the shadowing phenomenon into account, both in reflection and transmission. In addition, because no shadowing function in transmission exists in the literature, this function is presented here in detail. The model is reduced to the high-frequency limit (or geometric optics). The energy conservation criterion is investigated versus the incidence angle, the permittivity of the lower medium, and the surface rms slope.

Propagation-inside-layer-expansion method combined with physical optics for scattering by coated cylinders, a rough layer, and an object below a rough surface.

In this article, the fields scattered by coated cylinders, a rough layer, and an object below a rough surface are computed by the efficient propagation-inside-layer-expansion (PILE) method combined with the physical optics (PO) approximation to accelerate the calculation of the local interactions on the non-illuminated scatterer, which is assumed to be perfectly conducting. The PILE method is based on the method of moments, and the impedance matrix of the two scatterers is then inverted by blocks from a Taylor series expansion of the inverse of the Schur complement. Its main interest is that it is rigorous, with a simple formulation and a straightforward physical interpretation. In addition, one of the advantages of PILE is to be able to hybridize methods (rigorous or asymptotic) valid for a single scatterer. Then, in high frequencies, the hybridization with PO allows us to significantly reduce the complexity in comparison to a direct lower-upper inversion of the impedance matrix of the two scatterers without loss in accuracy.